The target antigens of anti-gamete transmission blocking antibodies against P. gallinaceum and P. falciparum form a complex of three proteins of approximately 250, 60 and 55 Kda in the malarial gamete membrane. The 60 and 55 Kda proteins are hydrophobic and probably embedded in the membrane; the 250 Kda protein is hydrophilic. In P. gallinaceum the transmission blocking Mabs recognize only the 250 Kda protein in P. falciparum the Mabs recognize only the 60 and 55 Kda proteins. The target epitopes appears to be destroyed by reduction. Recombinant clones of Lambda gt-11 containing P. falciparum DNA fragments from a mung bean nuclease digest have been isolated. One clone may contain DNA coding the 260 Kda protein, another the 60 and/or 55 Kda protein; a third such clone expresses a fusion protein which cross reacts with antibodies against ookinetes of P. gallinaceum. Isolate specific antigenic variation for the target epitope of one transmission blocking Mab has been confirmed in P. falciparum. Isolate specific differences in infectivity to different Anopheline species have also been demonstrated. Genetically distinct clones of P. falciparum are being hybridized in genetic recombination experiments during transmission through mosquitoes and primates. Malaria transmission studies are being conducted in Papua New Guinea and in Sri Lanka. The studies in Sri Lanka have shown that transmission blocking immunity is naturally induced during acute infections of P. vivax.